Add tests to lacheck linter

test/command_callback/test_tex_lacheck_command_callback.vader

@@ -0,0 +1,13 @@
+Before:
+  call ale#assert#SetUpLinterTest('tex', 'lacheck')
+
+After:
+  call ale#assert#TearDownLinterTest()
+
+Execute(Executable should default to lacheck):
+  AssertLinter 'lacheck', ale#Escape('lacheck') . ' %t'
+
+Execute(Should be able to set a custom executable):
+  let g:ale_tex_lacheck_executable = 'bin/foo'
+
+  AssertLinter 'bin/foo' , ale#Escape('bin/foo') . ' %t'